How I would work with the notifications is decided. But what I am thinking is,
What exactly the URL column here would contain? If I put an absolute URL for a post like

http://facebook.com/thomas/posts/123456

Wouldn't this be a problem? What if the user changes its username from thomas to something else tomorrow?
Just needed help in how can I work with destination URL, either on frontend (I'm using PHP) or backend (in database column itself)

I imagine facebook uses .htaccess to pass these variables to a PHP file. So it is actually calling get.php?user=thomas&post_id=123456. So you would not have a url field, but instead associate the post with a user_id and post_id. The username "thomas" can be looked up in the user table to get the user_id, so even if the user changes their name they would keep the same unique user_id. So if you wanted to display a url you would generate the url from this data.

thnx for the reply. just a moment before I decided to use object_id, and object_type. Object_id would be any id, eg: post_id,comment_id,etc, and object_type would allow me to format the URL at the server side. thnx mate :)
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EltonDec 29 '11 at 18:28